Catalytic desulfurization of petroleum hydrocarbons in a two stage autofining process



CATALYTIC DESULFURIZATION F TETROIJEUM HYDROCARBONS IN A IW0 STAGEAUTOFIN- ING PROCESS John Arthur Edgar May and John Rowland,'Snnbury-on- 5.5

Thames, England, assignors to The British Petroleum Company Limited,London, England, a British jointstockcorporation N0 Drawing. ApplicationMarch 21, 1956 Serial No. 572,785

Claims priority, applica'tionGreat BritainM'arch 22, 1955 '6 Claims. or.208-210) This invention relates to the catalytic dcsulfurization ofpetroleum hydrocarbons by means of the autofining process, the nature ofwhich is described inter alia in United States Patents Nos. 2,573,726,2,574,445-51 and 2,540,802. As set forth in these patents the autofiningoperation is carried out under a temperature selected between about650-800 F. and a pressure selected between 25-500 p.s.i. ga. with thetemperature and pressure being correlated with respect to one another toinsure a net production of hydrogen.

Almost complete desulfurization of the .lower boiling petroleumdistillates, such as naphtha and kerosene, is effected by once-throughtreatment of the distillate in the autofining zone, at a pressure of 100lb./sq. in.

In order to achieve adequate desulfurization on a once-through basis ofthe higher boiling petroleum distillates, such as gas oils, however, itis generally necessary. to carry out the process and. operate the plantunder the equilibrium pressure method described in United States PatentNo. 2,648,623. The equilibrium pressure obtainable with any particularfeedstock depends upon the particular catalyst employed, the temperatureand the space velocity. For a given catalyst, temperature and spacevelocity, the equilibrium pressure gradually falls from the maximumobtainable with fresh catalyst to a lower value, with decrease in thecatalyst activity. As set forth in Patent No. 2,648,623 in equilibriumpressure autofim'ng, the temperature is selected between 65-0800 F. andthe pressure is permitted to rise above 100 psi. ga. until the amount ofhydrogen produced equals the amount of hydrogen consumed at which pointthe system is in pressure equilibrium.

Plants suitable for the autofining of the lower boiling feedstocks maynot necessarily be adapted for operation at the higher pressures reachedwhen autofining under equilibrium pressure conditions, but it wouldnevertheless be desirable if the higher boiling petroleum distillatescould be adequately desulfurized in such plants.

It has now been found that higher boiling petroleum distillates that arenot adequately desulfurized by autofining on a once-through basis atpressures below the equilibrium autofining pressure of the distillateunder the autofining conditions of catalyst, temperature and spaceVelocity obtaining in the autofining zone, be further desulfurized byrecycling or reprocessing the product obtained from the first treatmentunder substantially the same conditions.

According to the present invention therefore, a process for thecatalytic desulfurization of a petroleum distillate, particularly of ahigher boiling petroleum distillate that cannot be adequatelydesulfurized by autofining alt pressures below the equilibriumautofining pressure, comprises autofining the distillate at a pressurebelow the equilibrium pressure and recycling the treated distillate tothe reaction zone, or reprocessing the treated distillate,

preferably under the same conditions, over a flesh charge of catalysts'The invent-ion is particularly applicable to the autofining of gasoils.

The catalyst employed is preferably 'of the kind comprising the oxidesof cobalt and molybdenum either as such or in combined form incorporatedwith a metal oxide support, usually alumina. The catalyst may withadvantage comprise a small amount, preferably between 0.1% and 6.0% byweight, of fluorine as described in United States patent applicationSer. No. 311,429, filed September 25, 1952, now US. :Patent No.2,800,429. "The use of .such a catalyst does not increase the degree of:desulfurization unless equilibrium pressure operation is employed, buteven .at lower pressures it has the effect of producing a greater netyield of hydrogen which may with advantage be used in other processes inthe refinery. The invention will now -be described with reference to thefollowingexamples:

Example 1 t A Kuwait gas oil was autofined in a pilot plant having amlncatalyst capacity under the following conditions:

The liquid product was washed with caustic soda solution and water toremove dissolved hydrogen sulfide and then reprocessed under the sameconditions over a fresh charge of catalyst. Two types of catalyst wereused, a catalyst consisting of the oxides of cobalt and molybdenumsupported on alumina and a catalyst of similar composition but activatedwith aluminum fluoride.

The results were as follows:

Mixed oxides Mixed Oxides of Cobalt and of Cobalt and MolybdenumCatalyst Molybdenum on alumina on alumina activated with aluminiumfluoride Chemical Analysis, g./100 g. of material stable 1,020" F.:

M00 15.75 14. 4 C00 3. 2 3. 2 F 0 3. 36 Liquid Product inspection dataAfter First Processing:

S.G. 60 F/60 F 0.8365 0.8390 13.1. (ASTM), C. 104 F.B.P. (ASTM), 0. 354355 Bromine No 10. 2 10.7 Aromatics (ASTM D875), percen v01 13. 5 12. 5Sulfur content, percent wt 0.54 0.55 Sulfur removal, percent.-- 57 56Gross Hydrogen make, s.c.f./b 136 Liquid Product inspection data AfterSecond Processing:

S.G. 60 F/60 F"..- 0. 8350 0. 8375 I.B.P. (ASTM), C. 89 94 F.B.P.(ASTM), C. 355 359 Bromine No 9. 8 11. 3 Aromatics (ASTM D875), percentvol 14.0 16.0 Sulfur content, percent wt- 0. 40 0. 44 Sulfur removal,percent 26 22 Gross Hydrogen make, s.c.i./b 28 41 3 Example 2 The samefeedstock as in Example 1 was processed under the same conditions as inExample 1, using the catalyst that. did not contain fluorine,forfive-processing periods, at the end of which the sulfur content of theproduct had been reduced to 0.17% wt. The results obtained were asfollows:

Run number 1 2 s 4 5 Duration, hours 25 22 21 21 20 Sulfur content ofproduct, ercent w 0. 17 Gross hydrogen make, s.c.f./b 133 34 26 14 12 Weclaim: Q '1. A process for the catalytic 'desulfurization underautofining conditions of a petroleum distillate that cannot beadequately desulfurized under autofining conditions on a once-throughbasis at pressures below the equilibrium autofining pressure of thedistillate obtainable under the autofining conditions of catalyst,temperature,

and space velocity existing in an autofining zone, which comprisescontacting the distillate in a reaction zone with adehydrogenation-hydrogenation catalyst and hydrogen derived solely fromthe distillate at a temperature between about 650-800 F., and at apressure below 25-500 p.s.i. ga., and recovering a distillate of stillfurther reduced sulfur content from the product of the second operation.

.2. A process in accordance with claim 1 wherein the autofiningconditions of the second stage reaction zone are substantially the sameas the first stage reaction zone.

3. A process in accordance with claim 1 wherein thedehydrogenation-hydrogenation catalyst is oxides of cobalt andmolybdenum on alumina.

4. A process in accordance with claim 3 wherein the catalyst containsabout 0.1% and 6.0% of fluorine.

5. A process in accordance with claim 1 wherein the distillate is a gasoil.

6. A process for the catalytic desulfurization under autofiningconditions of a petroleum distillate that cannot be adequatelydesulfurized under autofining conditions on a once-through basis atpressures below the equilibrium autofining pressure of the distillateobtainable under the autofining conditions of catalyst, temperature, andspace velocity existingin the autofining zone, which comprisescontacting the distillate in a reaction zone with adehydrogenation-hydrogenation catalyst and hydrogen derived solely fromthe distillate at a temperature between about 650800 F. and at a.pressure below the equilibrium 'autofining pressure obtainable under theselected operating conditions, recovering a distillate of reduced sulfurcontent, recycling the recovered" distillate back to the first reactionzone as the sole feedstock therein and in contact'with a freshdehydrogenation hydrogenation catalyst and in the presence of hydrogenderived solely from the recovered distillate, and under substantiallythe same conditionsof tempera- "ture and pressure as the initialtreatment, and recovering a.distillate of still further reduced sulfurcontent from the product of the second operation.

: I References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS FOR THE CATALYTIC DESULFURIZATION UNDER AUTOFININGCONDITIONS OF A PETROLEUM DISTILLATE THAT CANNOT BE ADEQUATELYDESULFURIZED UNDER AUTOFINING CONDITIONS ON A ONCE-THROUGH BASIS ATPRESSURES BELOW THE EQUILIBRIUM AUTOFINING PRESSURE OF THE DISTILLATEOBTAINABLE UNDER THE AUTOFINING CONDITIONS OF CATALYST, TEMPERATURE ANDSPACE VELOCITY EXISTING IN AN AUTOFINING ZONE, WHICH COMPRISESCONTACTING THE DUSTILLATE IN A REACTION ZONE WITH ADEHYDROGENATION-HYDROGENATION CATALYST AND HYDROGEN DERIVED SOLELY FROMTHE DISTILLATE AT A TEMPERATURE BETWEEN ABOUT 650-800* F,, AND AT APRESSURE BELOW THE EQUILIBRIUM ATUOFINING PRESSURE OBTAINABLE UNDER THESELECTED OPERATING CONDITIONS, RECOVERING A DISTILLATE OF REDUCED SULFURCONTENT, PASSINT THE RECOVERED DISTILLATE THROUGH A REACTION ZONE AS THESOLE FEEDSTOCK THEREIN AND IN CONTACT WITH ADEHYDROGENATION-HYDROGENATION CATALYST AND IN THE PRESENCE OF HYDROGENDERIVED SOLELY FROM THE RECOVERED DISTILLATE, AND AT A TEMPERATUREBETWEEN ABOUT 650-800 F,. AND AT A TEMPERATURE BETWEEN ABOUT REDUCEDSULFUR CONTENT FROM THE PRODUCT OF THE SECOND OPERATION.